Degree Type

Dissertation

Date of Award

2019

Degree Name

Doctor of Philosophy

Department

Agricultural and Biosystems Engineering

Major

Agricultural and Biosystems Engineering

First Advisor

Kurt A. Rosentrater

Abstract

Low-value biomass materials such as processing co-products and agricultural wastes possess abundant potential in value-added products production. The effort for utilization of these materials, especially as the substrate for fermentation process was limited by the low availability of fermentable sugar. This is due to the presence of lignin and hemicellulose in biomass structure, which entails appropriate pretreatment procedure to be conducted to expose the cellulose for the enzymatic reaction. Alkali-based pretreatments offer the attractive benefit of low inhibitor compound production. In this study, low moisture anhydrous ammonia (LMAA) pretreatment was conducted on selected biomass. Anhydrous ammonia, which is a gaseous state pretreatment agent, is naturally evaporated from the biomass after the process, therefore, have considerable potential to be recycled.

Selected materials were Distillers Dried Grains with Solubles (DDGS), corn gluten feed (CGF), and corn fiber (CF) from corn processing industries and oil palm frond (OPF) from oil palm plantation site. These materials are either sold at a relatively low price or with no value at all. The study was conducted using raw materials at different moisture contents (30 % and 50 % db.) and several incubation periods (24, and 72 h). The changes in the percentages of lignin, α-cellulose, and hemicellulose in each biomass along with the changes enzymatic digestibilities percentages were assessed. There was no significant difference in the results for most of the cases between materials incubated at 24 h with those incubated for 72 h. For the moisture content (MC) effect, higher MC (50 %) CGF and CF gave significantly higher percentages of α-cellulose than those of 30 % MC, while the case was vice versa for DDGS and OPF. The compositional results were compared to the enzymatic digestibilities results to determine the best LMAA operating conditions.

The results suggest that LMAA-treated DDGS, CGF, and CF could be additional feedstocks for the ethanol fermentation process. Other than fermentation into ethanol, glucose obtained from the hydrolysate of treated biomass is also a suitable substrate for butanol production or other fermentation-based products (i.e., biochemical). Works on cellulosic butanol production from a variety of raw materials are still lacking. Therefore, this study also attempts to assess the potential of LMAA-treated biomass for butanol production. OPF was used as the model substrate for all SuperPro Designer simulation works.

Economies of scale effect have shown that acetone-butanol-ethanol (ABE) fermentation plant at 95.34 × 106 L butanol/y size gave the minimum butanol production cost ($ 2.05/L). The major operating expenditures (OpEx) contributor was utilities (41 %), followed by materials cost (21.72 %). The major capital expenditures (CapEx) contributor was ABE fermentation section (67.17 %). Optimization of the processes through sensitivity analysis showed that by achieving higher enzymatic digestion yield in the hydrolysis process, the butanol production cost could potentially reduce to $ 1.63/L.

In the next part of the study, improvements on the models were applied, which includes the application of the CHP system to supply the heat and power for the entire plant and on-site cooling water generation. The simulation also conducted using different pretreatment (LMAA, autohydrolysis, SAA, and NaOH) and products separation (in-situ stripping, adsorption, pervaporation, and dual extraction) approaches. The results have shown that among all pretreatment tested, NaOH pretreatment gave the best yield, while the best yield among all products separation techniques was given by adsorption process. Nevertheless, the lowest butanol production cost of $ 1.58/L was recorded from the combination of LMAA pretreatment and in-situ stripping process. In several of the chosen models, by considering xylose content and its potential in butanol production, further reduction of butanol production costs was recorded with promising profit generated.

The final part of the study focused on the environmental impacts of all plant models simulated. The assessed impacts were global warming potential (GWP), ecotoxicity potential, and eutrophication potential. SAA pretreatment and pervaporation process recorded among the lowest GWP. LMAA in combination with in-situ stripping process recorded net energy value (NEV), net energy ratio (NER), and fossil energy ratio (FER) in the middle range among all other models simulated. The fact that these values were neither the lowest nor the highest might indicate that LMAA pretreatment possesses a potential for more detail study and commercialization. Techno-economic analysis and life-cycle assessment are necessary to determine the feasibility and sustainability of butanol production from cellulosic co-products and waste materials. The data is useful for further development effort of the processes.

Copyright Owner

Nazira Binti Mahmud

Language

en

File Format

application/pdf

File Size

213 pages

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